1. Technical Field
The present invention relates to a method for processing a substrate and in particular to a method for coating a polymer onto a substrate. Still more particularly, the present invention is related to a method for coating a polymer onto a square or irregular shaped substrate.
2. Description of the Related Art
It is often desirable to place a polymer coating, such as photoresist film, on a substrate to protect underlying film types, such as SiO.sub.2, aluminum, copper polysilicon, or silicon nitride. The polymer should be of a sufficient thickness on the substrate to provide an effective barrier to various etches, ion implantation, or mechanically induced damage. In placing coatings on a substrate, it is typically desirable to provide a very uniform film over the substrate.
One method in which thin uniform films of polymers are formed over a substrate involves introducing drops of liquid polymer onto a substrate, such as a circular wafer that is held by a vacuum chuck which can be set to rotate accurately at some predetermined speed. The wafer is then spun and centrifugal forces spread the liquid outwards with any excess being thrown clear of the periphery of the wafer. In a spin coating application, 90 to 95 percent of the polymer material is spun off and wasted.
Additionally, such a process is not very efficient when wafers, such as square wafers or other non-circular wafers, are coated with a polymer. In these cases, spin coating of polymers on the substrate may result in problems with uniformity at the corners of the substrate. Therefore, it would be advantageous to have an improved process for coating a polymer on a substrate that provides for uniformity and thickness over the entire surface and saves a considerable quantity of polymer.